1. Field of the Invention
The present invention relates to a method of controlling data flow from terminals in a centrally controlled communication system.
2. Prior Art
Several terminals T1 . . . T8, for example radio telephone units, PCs or other radio- or line-connected terminals are coordinated by a main station or central station. They can communicate, for example, by radio transmissions. It is also possible that the terminals directly communicate with each other but are coordinated by the central or main station ZE (FIG. 1). The terminals inform the central station of the state of their buffers, especially of the filling degree of the transmitting and receiving buffers. The central station ZE assigns the resources to the terminals. Methods for allocating transmission capacity in this kind of communication network are disclosed in German Patent Application 197 26 120.5; also in D. Petras, A. Krämling, “MAC protocol with polling and fast collision resolution for an ATM air interface”, IEEE ATM Workshop, San Francisco, Calif., August 1996; and in D. Petras, A. Krämling, A. Hettich, “MAC protocol for Wireless ATM: contention free versus contention based transmission of reservation requests”, PIMRC' 96, Taipei, Taiwan, October 1996. Usually a MAC channel access protocol (Medium Access Control) is used.
In order to request resources a terminal sends out a so-called resource request (RR), in which it informs the central station ZE of its needs. The RR message applies for an individual DLC (Data Link Control) connection and contains the number of messages that wait in the buffer of the terminal for transmission. It is important that the number of waiting messages in the buffer can exceed the capacity of an individual MAC transmission frame. The central station ZE confers the capacities of the individual phases of a MAC transmission frame again on the basis of individual DLC connections. For the down-link phase (central station in control of the terminal) it informs the terminal that is to receive the message. For an up-link phase (terminal in control of the central station) it informs which terminal may request a DLC connection at a predetermine time. For the direct mode channel (direct communication of the terminals with each other) the transmitter and receiver and the DLC connection are announced.
It should be noted that the RR message should always give the actual filling state of the buffer. In order to receive capacity according to the filling state as allocated by the central station ZE, it is not advisable for a terminal to transmit less than its actual filing state to the central station ZE, since the priority or urgency of the transmission is evaluated incorrectly by the central station under the circumstances.
Data flow control mechanisms already exist which operate so that a terminal can inform the central station ZE or the central station ZE can inform the terminal, that it would like to receive nothing for a predetermined DLC connection. This happens in connection with an ARQ (automatic repeat request) protocol and can prevent receiving buffer overflow.